Urea-nitrile complexes



Aug. 21, 1956 E. GORIN 2,759,916

UREA-NITRILE COMPLEXES Filed Feb. l, 1954 2 Sheets-Sheet l INVENTOR 1f/reif fiar/1V Ffm.

Aug. 21, 1956 E. GORIN UREA-NITRILE COMPLEXES Filed Feb. l, 1954 2 Sheets-Sheet 2 United States Patent' O UREA-NITRILE COMPLEXES Everett Gorin, Pittsburgh, Pa., assignor vto Socony Mobil Oil Company, Inc., a corporation of NewYork Application February 1, 1954, Serial No. 407,197

4 Claims. (Cl. 260-96.5)

This invention has to do with the separation of hydrocarbons and hydrocarbon derivatives of dilerent molecular configuration from mixtures containing the same, and also has to do With the preparation of new and novel compositions.

This application is a continuation-in-part of application Serial No. 115,515, filed September 13, 1949, now Patent No. 2,681,332.

I. FIELD OF INVENTION Numerous processes have been developed for theseparation of hydrocarbons and hydrocarbon derivatives of diterent molecular configuration by taking advantage of their selective solubility in selected reagents or solvents from which they may later be separated. Exemplary of hydrocarbon separation procedures is the Edeleanu process, wherein paratiinic materials are separated from aromatics by virtue of the greater solubility of aromatics in liquid sulfur dioxide. Lubricant oil solvent refining processes, solvent deasphalting, solvent dewaxing and the like are further examples of the separation of hydrocarbons of dierent molecular configuration.l Typical of selective solvent procedures for separating hydrocarbon derivatives is the separation of parain wax, monochlorwax and polychlorwaxes, with acetone as the selective solvent.

This invention is concerned with the general field outlined above, but based upon a different and little-known phenomenon, namely, the ditfering ability of hydrocarbons and hydrocarbon derivatives to enter into and to be removed from certain crystalline complexes. As used herein, the term complex broadly denotes a combination of two or more compounds.

This invention is predicated upon the knowledge that urea forms complex crystalline compounds to a varying degree with various forms of hydrocarbons and hydrocar bon derivatives.

II. PRIOR ART For some years it has been known that various isomers of aromatic hydrocarbon derivatives form` complexes with urea. Kremann (Monatshefte f. Chemie 28, 1125 (1907)) observed that complexes, designated as double compounds, of urea and the isomeric cresols are stable at different temperatures. Schotte and Priewe (1,180,859) later separated meta-cresol from the corresponding para isomer by selectively forming a meta-cresol-urea complex, which was described as an addition compound", the latter compound was separated from the para isomer and then split up by distillation or with water or acid to ohtain pure meta-cresol. The addition compound of vmetacresol and urea was shown thereafter to have utility as a disinfectant (Priewe-1,933,757). Bentley and Catlow (1,980,901) found a number of aromatic amines conf taining at least one basic amino group capable `of fprining double compounds with certain isomeric phenols. It has also been shown that trans-oestradiol can be separated from the corresponding cis-compound by forming a diflicultly soluble compound of urea and trans-oestradiol (Pri-eweZ 00,134).

The forces between urea and the compounds of the foregoing complexes are due to specific chemical interaction between the various functional groups.

One heterocyclic compound, 2:6 lutidine, has been found to form a crystalline compound with urea, thus affording a means of separating the lutidine from betaand gamma-picolines (Hemd-2,295,606).

Comparatively few aliphatic hydrocarbon derivatives have been known to date to form complex compounds with urea. In German patent application B 190,197, IV d/ l12 (Technical Oil Mission, Reel 143; Library of Con gress, May 22, 1946), Bengen rescribed a method for the separation of aliphatic oxygen-containing compounds (acids, alcohols, aldehydes, esters and ketones) and the straight chain hydrocarbons of at least six carbon atoms from mixtures containing the same, the method being predicated upon the ability of such compounds and hydrocarbons to form Additions-Produkt with urea. In the Technical Oil Mission translation of the Bengen application, however, the urea complexes were designated adducts, which term apparently stems from the anglicized addition product.

lll. DEFINITIONS From the foregoing discussion of prior art (II), it will be clear that a variety of terms have been applied to urea complexes. The latter have been rather loosely described as double compounds, addition compounds, dilicultly soluble compounds, Additions-Produkt, and adducts All of these terms are somewhat ambiguous in that they have also been used to described products or complexes of diterent character than the urea complexes under consideration. This is particularly so with the term adduct, and the related term unadducted material. While the term adduct is simple and convenient, it is an unfortunate designation, inasmuch as it confuses these complexes with other substances known in the chemical art. Specifically, adduct has been applied to Diels-Alder reaction products, formed by re,- action of conjugated diolefins and oletins and their derivatives. As is well known, Diels-Alder products, as a rule do not revert to their original constituents when heated or treated with water, acids, solvents, etc. Morel over, the term dduct has been defined earlier as The product of a reaction between molecules, which occurs in such a way that the original molecules or their residues have their long axes parallel to one another. (Concise Chemical and Technical Dictionary). Further ambiguity is introduced by the term adductiom which has been defined as oxidation (Hackh.)

To avoid the foregoing conicting terminology, several related terms have been coined to deiine with greater speciiicity the substances involved in the phenomenon under consideration. As contemplated herein and as used throughout the specification and appended claims, the following terms identify the phenomenon:

Plexad-a revertable associated complex comprising a plexor, such as urea, and at least one other compound; said plexad characterized by reverting or decomposing, under the influence of heat and/or various solvents, to its original constituents, namely, a plexor and at least one plexand.

Plexand-a compound capable of forming a plexad with a plexor, such as urea; compounds of this character differ in their capacity to form plexads, depending upon various factors described hereinafter.

Antiplex-a compound incapable of forming a plexad with a plexor.

Plexor-a compound capable of forming a plexad with a plexand; such as urea.

Plexate-to form a plexad.

Plexation-the act, process or etect of pleXating.

IV. OUTLINE OF INVENTION It has now been discovered that certain terminallysubstituted straight chain compounds, plexands, form plexads with urea. It has also been discovered that, by selective plexation with urea, a terminally-substituted straight chain compound can be separated, in the form of a plexad, from a mixture containing the same and a non-terminally-substituted compound. This separation procedure is effective also when the parafn derivatives have the same number of carbon atoms, as in the case of isomers, or have a different number of carbon atoms. Selective plexation is also effective when the terminal and non-terminal substituents are different, and the number of carbon atoms et' the substituted parains are the same or different.

The substituent groups which may characterize the terminally-substituted compounds are inorganic and organic groups of the following character:

(a) Halogen: F, Cl, Br and I;

(b) Nitrogen-containing: NH2, NH(R), NRz, NO2, NOH, CN, CONHz, CONI-HR), CON(R)2, CNO, CNS, NCO, NCS, etc., wherein R is a hydrocarbon radical;

(c) Sulfur-containing: SH, SR, SOaH, OSOaH, SOzH,

SOzR, wherein R is a hydrocarbon radical, SOzZ Wherein Z is a halogen atom, etc.

(d) Cyclic: cycloalkyl such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, chlorcyclohexyl, etc.; aryl such as phenyl and chlorphenyl; hetero such as thienyl C4H3S, furyl C4H3O, pyrryl C4H4N, pyridyl C5H4N, thiazyl CaHzNS, pyrazolyl CsHsNz, piperyidyl CsHioN, etc.;

(e) Alkenyl: methylene, vinyl, etc.;

(f) Haloalkyl: dichlormethyl ClzCH-, etc.

As contemplated herein, the invention makes possible the separation of one or more plexands from a mixture containing the same, such plexand or plexands being separated in the form of a plexad or plexads which, as described in detail hereinbelow, revert to the plexor, urea, and the plexand or plexands under certain conditions. The separation, therefore, is an excellent means for obtaining, in pure or concentrated form, one or more plexands or antiplexes whichever is the desired material. The invention also provides a means of forming new compositions of matter, namely, a number of plexads which may be used as a source of a plexor, urea, or as a source of a plexand.

V. OBJECTS It is an object of this invention, therefore, to provide an effective means for separating hydrocarbons and hydrocarbon derivatives of different molecular configuration from mixtures containing the same.

It is also an object of this invention to selectively separate terminally-substituted straight chain compounds yfrom mixtures containing the same.

A further object is to separate a terminally substituted straight chain compound from a mixture containing the same and a non-terminally substituted isomer.

Still another object is to separate a terminally-substituted straight chain compound from a mixture containing the same and a non-terminally-substituted straight chain compound having a different number of carbon atoms.

An additional object is to separate a terminallysubstituted straight chain compound from a non-terminally-substituted compound, wherein the substituents are different and the number of carbon atoms of the respective compounds are the same. A related object is to separate a terminally-substituted straight chain compound from a non-terminally-substituted compound, wherein the substituents are different and the number of carbon atoms of the respective compounds are different.

A further object is to separate a non-terminally-substituted compound from a mixture containing the same and a second non-terminally-substituted compound less susceptible to plexation.

Another important object is the provision of a continuous method of separation of said plexands and antiplexes, which method is flexible, capable of relatively sharp separation, and not highly demanding of attention and of utilities such as heat, refrigeration, pumping power, and the like.

An additional object is to provide a plexand or plexands substantially free of an antiplex or antiplexes. A corresponding object is the provision of an antiplex or antiplexes substantially free of said plexand or plexands.

Another object is to provide a new and novel class or sub-classes of plexads comprising a plexand and urea. A related object is the provision of a new and novel class or subclasses of plexads comprising a secondary plexand and urea.

Other objects and advantages of the invention will be apparent from the following description.

VI. INVENTION IN DETAIL As indicated above, it has been found that the foregoing objects are achieved by plexation with urea (a plexor) of a plexand or plexands.

(I) Plexands Plexands contemplated herein are represented by the general Formula A:

(A) X(CH2).CH3

wherein n is a whole number and wherein X is a substituent group of the character described above, with n and X being interrelated.

The substituent group X may be any of the types outlined above subject, however, to one important restriction, namely, that of geometrical size. Two dimensions are of importance in determining the nature of the separation that may be obtained between compoundsplexands and antiplexes-given above. The first dimension is the cross-section of the group (X) taken in a direction perpendicular to the bond joining the group (X) to the parent hydrocarbon. This distancewidthis taken at the Widest portion of the group and may be conveniently given a quantitative measure as the distance from between outer covalent radii of the two most widely separated atoms along the cross-section of the group where the covalent radii are those given by Pauling (Pauling-Nature of the Chemical Bond; Cornell University Press; Ithaca, New York; 1939). The second distance-lengthis the projection along the bond joining the group to the parent hydrocarbon of the distance from the center of the carbon atom to which the group is attached, to the center of the atom whose covalent radius shell extends furthest in the direction of said bond, plus the covalent radius of said bond.

The rst distance determines the length of the aliphatic chain required to obtain plexation at room temperature (25 C.) with a saturated urea solution, a plexor, when the group (X) in question is attached to the terminal carbon atom of the aliphatic chain. ln the case of composite groups of the type -COY, -CH2COY and -CH2Y, where Y is a non-aliphatic radical such as chlorine or amino, the =CO, -CHzCO and -CHaconstituents, respectively, are considered as part of the aliphatic chain and the width computed is that for the radical Y.

The widths of a number of typical groups computed according to the method given above are listed in order of size in Table I below:

TABLE I.-Width" of various groups in A 1. SH 2. 67 l.. 28 -NO2.. 3. 32 l. 98 -S O 3B'. 3. 69 1. 98 Thienyl..- 4. 38 2. 11 Cyclohexy 4. 74 11 Phenyl.-. 5.15 2. 28 2 or 3 Methyl C yclohexyl. 5. 49 2. 66 O- or M-tolyl 6. 09

The correlation between the width of the group and the length of the aliphatic chain required for plexad formation at room temperature is an approximate one. T his relationship depends to some extent upon the nature of the group (X) as well as upon the width of the group (X). For example, in the case where two groups (X) are the same size, the group which imparts a higher melting point to the substituted parain will form the stronger plexad, i. e., will form a plexad when the aliphatic chain is somewhat shorter in length.

Only the carbon atoms in the chain are considered to contribute to the chain length, that is, atoms such as oxygen, sulfur, nitrogen, etc., are not included in the atom total. Accordingly, then, the straight chain compounds contemplated herein include straight chain aliphatic hydrocarbons and straight chain aliphatic hydrocarbons in which one or more of the carbon atoms of the chain have been replaced by such atoms as oxygen, sulfur, nitrogen, and the like.

It is possible, however, to give the unequivocal limits for the relation between width of the group (X) and size of the carbon chain required for plexation with urea at room temperature, C. These limits are set forth in Table II below:

TABLE II.CORRELATION BETWEEN 'WIDTH" OF GROUP (X) AND MINIMUM CHAIN LENGTH FOR UREA. PLEXATION AT 25 C.

Minimum hain Group Width" Length,

(in A) Number of Carbon Atoms It is to be understood that these limits apply for plexation at temperatures of the order of about 25 C. The minimum number of carbon atoms in the chain is generally lower for plexation at lower tempera-tures, but generally not more than one or two carbon atoms lower. ln the same vein, for an increase in temperature, a correspondingly higher number of carbon atoms will be required in the carbon chain.

By way of illustration, the following compounds are typical pleXands:

Cil

Cyanate and isocyanate--n-hexyl cyanate; n-hexyl isocyanate; n-decyl cyanate; n-decyl isocyanate; n-hexadecyl cyanate; n-hexadecyl isocyanate; etc.

Thiocyanate and isothiocyanate-ndecyl thiocyanate; n-decyl isothiocyanate; n-octadecyl thiocyanate; n-octadecyl isothiocyanate; etc.

(c) Sulfur-containing compounds:

Mercapto-n-octyl mercaptan; n-dodecyl mercaptan; n-hexadecyl mercaptan; n-octadecenyl mercaptan; etc.

Suldo (SR)-methy1, n-octyl sulfide; butyl, n-

dodecyl sulfide; amyl, n-hexadecyl suliide; etc.

Sulfato--n-dodecyl sulfate; n-hexadecyl sulfate; etc.

Sulfonyl halide-n-decyl sulfonyl chloride; n-dodecyl sulfonyl bromide; n-hexadecyl sulfonyl iodide; etc.

(d) Cyclic substituent: l-cyclopropyl-n-octadecane; 1- cyclohexyl-nhexadecane; l-phenyl-n-octadecane; 1- thienyl-n-octadecane; etc.

It is to be understood that terminally-substituted straight chain compounds containing a second terminal substituent on the opposite terminal carbon atom, are also contemplated herein as plexands. Such disubstituted compounds are also subj'ect to approximately the foregoing relationships of terminal group width and chain length. Compounds of this character are represented by the following general formula:

wherein n is a whole number, and X and X are the same or different and as defined above.

illustrative of such compounds are:

1,10-dichlor-n-decane; LS-n-octane diamine; 1,10-n-decane diamide; 1,12-n--dodecane dithiol; 1,18-dsulfo-n-octadecane; etc.

Another class of compounds contemplated herein as plexands are those having a non-terminal substituent, and being represented by general Formula B:

wherein r and m are integers, the sum of which is equal to n-Z, and n and X are as defined above.

The length, rather than the width, of the substituent group (X) roughly determines the minimum carbon chain length required for plexation of the foregoing plexands (B) namely, non-terminally substituted straight chain compounds. These compounds may be considered secondary plexands. The minimum chain length is also to some extent a function of the position substituted as well as of the chemical nature of the group. Thus, in compounds yof this type, the minimum chain length required for plexation is Adetermined by the length of group H3C(CH2)r-, if r is small enough so that this alkyl group is shorter in length than the substituent group (X). It is possible, bearing this relationship in mind, however, also to give rather wide limits in the correlation of group length with the minimum chain length required for plexati'on. Themlengths of various groups are given in Table III, below, while the correlation of chain lengths vih group lengths is given in Table lV, also provided e ow:

TABLE III 2. O6 CH2 Cl 2.17 CN it 2. 61 3. 37 2. 76 3. 43 2. -cyclohexyl (Average 5. 09

con figuration) 3. 05 -pheny 5. 69

TABLE IV.-CORRELATION BETWEEN LENGTH OF NON-TERMINALLY-SUBSTITUTED GROUPS AND MINI- MUM CHAIN LENGTH REQUIRED FOR UREA PLEXA- TION AT 25 C.

Minimum Chain Length, Number of Carbon Atoms Length Group (in Ao) 2-chloro-n-tetracosane; Z-bromo-n-tetracosane; 2-amin-o-n-decane; 2-nitro-n-octadecane; etc.

Considering the relationships shown by Tables III and IV, it will be seen that 2-chloro-n-octadecane, for example, will form a plexad with urea at about 25 C. This, then, illustrates a plexad comprising a secondary plexand and urea. A further illustration is a non-terminal bromide such as Z-bromo-tetracosane.

By way of illustration, it follows from the foregoing that l-bromo-n-tetracosane is separated readily from a mixture of the same and an isomer such as 2-brorno-ntetracosane. This is typical of a separation of a compound represented by general Formula A, above, separated from a compound represented by general Formula B, above, wherein the halogen atoms and the number of carbon atoms thereof are the same.

A further illustration stemming from the foregoing data is the eficient separation of l-chloro-n-octadecane from a mixture of the same and 2-chloro-n-hexadecane; or a mixture of the same and 2-chloro-n-cosane thus demonstrating the separation of a compound represented by general Formula A, above, from a compound represented by general Formula C:

(C) HaotCHnfCHHomoHi wherein the sum of r-f-nt is other than n-2, and wherein the halogen atom is the same as in (A).

As mentioned earlier, two parain derivatives of the same chain length but having different substituents can be separated by plexation. This feature is illustrated by selective plexad formation of l-chloro-n-octane in a mixture containing the latter and 2-bromo-n-octane. This may be referred to as the separation of a monohalide represented by general Formula A from a monohalide represented by general Formula D:

wherein the sum of r-l-m is equal to n-2, and wherein the halogen atom X is different from X in (A).

Still another separation which is effected readily is that of l-chloro-n-octane from a mixture containing the same and 2-bromo-n-heptane or a mixture of the same and 2-bromo-n-nonane, that is, wherein the number of carbon atoms and the halogen atoms are different. This is the separation `of a compound represented by general Formula 8 A from a compound represented by general Formula E: (E) HsCshHHf-CH:

wherein the sum of r-i-m is other than n-2 and wherein the halogen atom X is different from X in (A).

.Among the various amines shown above are straightchain secondary amines represented by general Formula F:

N-H R( wherein Ri and R2 are n-alkyl groups or terminallv-substituted n-alkyl groups, and wherein the total number of carbon atoms of R1 and Rz is at least about eight.

Amines of the type represented by (F) form strong plexads with urea, in contrast with secondary amines in which R1 and/or Rz are branched-chain alkyl groups or are other than terminally substituted alkyl groups; the latter amines have a much lower capacity to form plexads with urea. For example, dien-butyl) amine, di- -namyl) amine, di{n-decyl) amine, din-dodecyl) amine and dn-octadecyl) amine readily formed plexads when agitated with a urea-saturated water solution at 25 C. In contrast, diZ-ethyl-hexyl) amine did not form a plexad under the same conditions. This difference in behavior makes possible the preferential separation of straight-chain amines from branched-chain amines such as are obtained in the reaction of primary and secondary alcohols, or halides with ammonia. This is illustrated by treating a mixture of din-octyl) amine and din-ethylhexyl) amine with ya urea-saturated water solution at 25 C.; `the di n-octyl) amine formed a plexad and the diZ-ethylhexyl) amine did not.

Secondary amines represented by (F) are separated from tertiary amines of the character shown by general Formula G:

Rg-N R:

wherein R1, R2 and R3 are the same or ditIeren-t, straightchain or branched-chain alkyl groups.

For example, under the conditions mentioned directly above, tritn-butyl) amine failed to form la plexad. Thus, secondary amines (F) are separated from tertiary amines (G) when contacted with urea. When a mixture of dit-n-butyD amine and 'tri{nbutyl) amine is agitated with a saturated urea solution, `di{nbutyl) amine is selectively plexated. This procedure is particularly advantageous in separating amines obtained when ammonia is reacted with straight chain primary alcohols, particularly alcohols containing twelve or more carbon atoms, for in the latter case separation by distillation is diicult to effect without concurrent decomposition of product.

(2) Antplex An antiplex, as defined above, is a compound incapa-l ble of a forming a plexad with `a plexor, such as urea.

(3) Plexor The plexor used herein is urea, which is in solution in a singleor multiple-component solvent. This solution should range from partially saturated to supersaturated at the temperature at which it is contacted with a plexand or with a mixture containing one or more plexands and antiplexes, and, in many cases, it will be found convenient to suspend a further supply of urea crystals in the solution, handling it as a slurry. For gravity or centrifugal separation, it is convenient to use a solvent of such a specific gravity that after the formation of a desired amount of plexad, the specific gravity of the solvent phase will be diterent from that of the plexad phase and of the antiplex phase to a degree suffi- 9 cient to permit separation by gravity, centrifuging, etc.

The solvent should be substantially inert to the plexand' and to the compounds of the mixture and also to the urea. Preferably, it should also be heat stable, both -alone and in contact with urea, at temperatures at which the desired plexad is not heat stable.

As indicated above, the solvent may be either singleor multiple-component. It is sometimes convenient, particularly where the plexad is separated by gravity, to utilize a two-component system, as water and an alcohol, glycol, amine or diamine, and preferably a lower ali-` phatic alcohol such `as `methanol or ethanol, or a watersoluble amine such `as piperidine. Such a solvent, partially saturated to supersaturated with urea, lends itself readily to a continuous process for separation by plexation.

Solutions containing suflicient water in order to minimize the solubility of the hydrocarbon derivativesin the urea solvent are often employed. The minimum quantity of water required in such instances depends upon the polarity and lthe molecular weight of the hydrocarbon derivative, Ior plexand, being treated and, in general, this quantity will be greater with more polar plexands and with lower molecular weight compounds.

In certain `cases the use of single-component solvents is advantageous. Single-component solvents other than alcohols may be employed, although they are normally not `as useful as the lower aliphatic alcohols. Glycols may be employed as :single solvents, yet ethylene glycol is generally not suitable in gravity separation operations due to the high density of the urea-saturated solvent. The higher glycols and particularly the butylene glycols may be advantageously employed. Diamines such as diamino-ethane, -propane and -butane may likewise be employed. Additional useful solvents include forrnic acid, acetic acid, formamide and acetonitrile, although the first three of these are subject to the same limitation as ethylene glycol.

Solvents generally useful when mixed with suiicient water, ethylene glycol or ethylene diamine, to render them substantially insoluble in the derivatives being treated, are yselected from the class of alcohols such as methanol, ethanol, propanol, etc.; ethers such as ethylene glycol dimethyl ether; and amines such as triethylamine, piperidine. When gravity separation is employed, the mixed solvent is preferable subject to lthe restriction that the density .after saturation with urea must be less than 1.0-1.1.

(4) Typical Separmons In =order that this invention may be more readily understood, rtypical separations are described below with reference being made to the ldrawings attached hereto.

(a) Separation of plexand from antiplex-'The procedure which may be employed in effecting the separation of terminally-substituted from non-terminally substituted, straight chain hydrocarbons may be essentially the same as that described in copending application Serial No. 4,997, filed January 29, 1948. The plexand obtained in decomposing 'the plexad obtained in a urea treatment of a mixture of terminally-substituted and nonterminally-substituted, straight chain hydrocarbons is very pure, provided the substituent group and Ithe aliphatic chain length are of such dimensions that only the terminally-substituted hydrocarbon forms a plexad and provided the plexad be carefully freed of occluded antiplax before it is decomposed. For example, substantially pure l-halide is separated from lthe plexad obtained in the treatment of terminally-substituted and nonterminally-substituted chlorides or bromides of normal paraflins containing from 8-16 carbon atoms.

In Figure 1, a charge comprising a plexand and an anti-Plex, for example 1-bromo-n-octane and 2-bromo-noctane, respectively, enters through line 1, to be contacted with urea solution from line 2, and the charge and solution are intimately mixed in mixer 3. In case the charge 10 undergoing treatment is rather viscous at the temperature of plexad (1-bromo-n-octane-urea) formation, it is advisable to provide a diluent, such as for example, a naphtha cut which may be recycled within the process, as described later, and joins the charge from line 4. Diluent make up is provided by line 5.

From mixer 3, wherein there is achieved an intimate mixture of urea solution and charge, the mixture flows through line 6, heat exchanger 7, and cooler 8 into settler 9. There may be some or a good portion of plexad (1-bromo-n-octane-urea) formed in mixer 3, but in general, it is preferred to operate mixer 3 at a temperature somewhat above that conducive to heavy formation of plexad. Then, in heat exchanger 7, the temperature of the mixture is reduced, and in cooler 8 adjusted, so that the desired plexad is formed. It will be recognized that this showing is diagrammatic, and that the heat exchangers and coolers, heaters, etc., shown will be of any type suitable, as determined by the physical characteristics of the materials being handled.

From cooler 8, the plexad-containing mixture flows into settler V9. This settler is preferably so managed that there is an upper phase of antiplex (2-broino-noctane), an intermediate phase of urea solution, and'a lower region containing a slurry of plexad in the urea solution. 'Ihe incoming mixture is preferably introduced into the solution phase, so that the antiplex (Z-bromon-octane) may move upward and plexad downward, through some little distance in the solution, to permit adequate separation of plexad from antiplex and antiplex from plexad.

Antiplex will be removed from settler 9 by line 1t) and introduced into fractionator 11, wherein the diluent is removed, to pass overhead by vapor line I2 and eventually to use through line 4. Recovered antiplex (Z-bromo-noctane) passes from the system through line 13. Obviously if no Idiluent be used, fractionator 11 will be dispensed with.

Plexad and urea solution, withdrawn from settler 9 through line 14, are passed through heat exchanger 7 and heater 15 to enter settler 16 through line 1'7. In this operation, the temperature is so adjusted that the plexand (1-bromo-n-octane) is freed from the plexad and, in settler 16, the plexand rises to the top to be recovered from the system by means of line 18. The urea solution, thus reconstituted to its original condition by return to it of that portion of the urea which passed into plexad, is withdrawn from settler 16 by line 2 and returned to process. Naturally, in a process of this kind there are minor mechanical and entrainment losses of urea solution, etc., and urea solution makeup is provided for by line 19.

In many cases, the separation of plexad and solution from antiplex may be conducted with greater facility in a centrifuge operation. Such a setup is shown in Figure 2, wherein only the equivalent of that portion of Figure 1 centering about settler 9 is reproduced. Again in diagram form, the cooled mixture containing antiplex, plexad and urea solution enters centrifuge 2@ through line 6. In many cases, it will be desirable to utilize a carrier liquid in known manner in this operation and that liquid may be introduced by line 21. Antiplex will be carried off through line 10, and plexad, urea solution, and carrier, if present, pass through line 22 to a separation step, which may include washing and may be carried out in a settler, a filter, or another centrifugal operation, which separation is indicated diagrammatically at 23. Carrier liquid, if used, returns through line 24, and urea solution and plexad pass through line 14. (Note: lines o, iii and 14 are the same lines, for the same functions, as in Figure 1 and are identically numbered.)

(b) Separation of one plexand from a second plex- Ind.-In the case where both the terminally-substituted and non-terminally-substituted compounds form plexa-ds, a concentration of the terminally-substituted compound will be obtained. The sharpness of separation of the terminally-substituted compound will be greater, the greater the difference in the strength of the plexads formed with the two types of pure compounds. In general, this will be greater, the shorter the carbon chain length of parent hydrocarbon. For example, substantially pure l-bromo-n-octane can be obtained from a mixture with 2-bromonaoctane in a single plexation. It is more diiicult, however, to obtain separation between lchloro-n-octadecane and 2-chloronoctadecane.

The following serves to illustrate a procedure for o`o taining sharp separation between one plexand, l-chloron-octadecane, and a second plexand, 2-chloro-n-octadecane, the latter behaving as la secondary plexand in forming a plexad. This procedure is similar to a sweating or a solvent sweating procedure used in the rening of slack waxes, and is shown diagrammatically in Figure 3.

In Figure 3, a slurry of solid urea in a saturated urea solvent, which is preferably an aqueous alcoholic solution, is pumped from line 31 into a turbo mixerr32 where it is agitated with a mixture 1- and 2-chloronocta decanes, which enters through line 33. An immiscible solvent charged through line 34 is also preferably employed, such as a light cut from a straight run naphtha in case the compounds of the mixture treated have: (1) a relatively high viscosity; (2) an `appreciable solubility in the urea solvent; or (3) greater density than the urea solvent. The amount of excess solid urea employed should be sufficient so that after the plexation is completed the urea solvent remains substantially saturated with urea.

Internal cooling means may be employed in 32 to further cool the mixture and remove the heat evolved during the plexation. The temperature employed in 32 will depend upon the chain length of the plexand and secondary plexand. If the chain length is such that it is not more than one or two `carbon atoms greater than the minimum required to obtain plexation with the pure plexand at 25 C., then temperatures in the range of -10 to 20 C. should be employed. If the chain length is from two to six carbon atoms greater than the minimum, temperature in the range of -30 C. should be employed; and if the chain length is greater than six carbon atoms beyond the minimum, temperatures from 25-50 C. may be employed. It will be apparent, then, that conditions of operation vary considerably, conditions selected being those appropriate for the formation of the desired plexad or plexads.

The slurry of plexad, urea solvent and secondary plexand is pumped, by means of pump 36, through line 3S and cooler 37 wherein it may be further cooled if desired, and into gravity settler 38. In settler 38 the secondary plexand plus naphtha solvent rises to the top and is withdrawn through line 39 into fractionator 40. The .secondary plexand, predominantly 2-chloro-n-octadecane, is removed as bottoms from fractionator 40 through line 41. The naphtha solvent is taken from fractionator 4t) through line 42, cooler 43, tank 44 and line 45 to be employed in solvent sweating Zone 46. Naphtha solvent may also by recycled to fractionator 40 through line 47, by means of pump 48.

In settler 38, the slurry of plexad in urea solvent is taken ol through line 49, heat exchanger 50 and heater 51 into solvent sweating zone (or mixer) `46. A portion of the clear urea solvent may be removed from the center of 3S and recycled, through line 51 and pump 52, to mixer 32. if desired.

It is to be understood that the gravity settler 38 may be replaced by other separation means such as a centrifuge or rotary lter, etc.

The mixture of solvent and plexad is heated in solvent sweating zone 46 to a temperature sufcient to decompose the major portion of the plexad of the 2-chloro-noctadecane, while preserving the major portion of the plexad of 1chloronoctadecane- The temperature em- 12 ployed in zone 46 is related to that employed in mixer 32, and will generally be maintained from 10-20 C. higher in Zone 46 than in mixer 32.

The partially decomposed plexads, urea solvent, and naphtha mixture is passed from zone 46 through line 53 to settler 54. The naphtha containing plexand, 1-chloronoctadecane, and some secondary plexand, Z-chloro-n-octadecane, is recycled through lines 55 and 33 to mixer 32. The slurry of undecomposed plexad is withdrawn from the bottom of settler 54 through line 56, heat exchanger 57, heater 58 into settler 59. The plexad is thus heated hot enough to cause complete decomposition or reversion of the plexads and solution of the urea in the urea solvent. Temperatures in the range of 55-85" C. are generally suitable.

Plexand, l-chloro-n-octadecane, contaminated with naphtha which had been occluded on the corresponding plexad (l chloro n octadecane urea) is withdrawn through line 60 into fractionator 61. Naphtha is taken oft overhead from fractionator 61 through line 62, cooler 63, tank 64, pump 65 and line 66, to mixer 31. A portion of the naphtha may also be recycled to fractionator 61 through line 67. Plexand is recovered as bottoms through line 68.

Urea solution is recycled from the bottom of settler 59 through line 69, pump 70, heat exchangers 57 and 50, and line 51.

Plexand of any desired purity may be obtained by either: (l) increasing the fraction of the total plexad decomposed in the solvent sweating zone (46), or (2) including a multiplicity of alternating solvent sweating zones (46) and settling zones (54) operated in series.

VII. ILLUSTRATIVE EXAMPLES The following examples serve to illustrate, and not in any sense limit, the present invention.

(a) T ermnally-substtuted straight chain parans general Formula A.-A number of such paraffin derivatives of varying chain length were agitated for several hours with water or with aqueous methanol solutions saturated with urea, and plexad formation was evidenced by resulting precipitate. The results are summarized in Table V, below, and the minimum chain length required for plexation found experimentally is compared with the correlations given in Table IV. Table V is as follows:

TABLE v.-CoMPARIsoN 0F MINIMUM CHAIN LENGTHS REQUIRED FOR UREA PLEXATIONAT 25C. FOR HYDRO- CARBONS-l DETERMINED EXPERIMENTALLY WITH THOSE GIVEN IN TABLE II. PLEXAD FORIVIATION- It will be noted from the data set forth in Table V that, in all instances, experimental values found for the minimum chain length are within the limits specitied in Table II.

(b) Comparison of equilibrium values in the plexation of compounds of general Formulas (A) and (B).- Plexation of a plexand, dissolved in an antiplex such as a suitable branched chain hydrocarbon solvent, with a saturated urea solution proceeds until the concentration of the plexand is reduced to a certain minimum concentration whichmay be termed the equilibrium concentration. In general, the equilibrium concentration is lower, the lower the temperature of plexation and is dependent only upon the temperature and not upon the solvent for the plexand, provided the urea solution is maintained saturated with urea and provided the plexandsolvent phase can be regarded as an ideal solution.

13 Equilibrium values were determined for several p-airs of compounds, (A) and (B), by agitating solutions of varying concentrations of the` substituted hydrocarbon in iso-octane with a 70% methanol-30% water solution saturated with urea and noting the minimum concentration required for plexad formation. The results are summarized in Table Vl, below.

TABLE VI.EQUILIBRIUM VALUESIN THE UREA PLEXA- From the data shown in Table VI, it will be noted that the terminally-substituted compound, (A), lforms a plexad, while the non-terminally-substituted compounds, (B), do not form plexads. When the compound (B) does not form a plexad, relatively sharp separation can be obtained between componds (A) and (B) in a single plexation.

(c) Separation of 1bromonoctane and 2brom0noctane.-The following solution was contacted with urea, in a reaction vessel: equal parts by volume of 1bromon octane, 2-bromo-n-octane and 2-methyl pentane.` A portion, 45 parts by volume, of this solution was agitated at room temperature C.) with 50 parts by volume of an aqueous 80% methanol solution saturated with urea at 45 C. A plexad was formed and settled to the bottom of the urea solution. The upper layer, free of plexad, was decanted from the lower layer. The upper layer was distilled whereupon Z-methyl pentane was distilled off, and the composition of the bromide residue was determined by refractive index measurement.

The plexad was ltered from the urea solutionwashed with 2-methyl pentane and then decomposed with Water to urea and plexand. The recovered plexand was distilled to remove Z-methyl pentane and the residue was analyzed for the bromo-octanes by refractive index.

No 2-bromo-n-octane was removed from the original solution, while the bromo-n-octane content was reduced from 33.3 volume per cent to its equilibrium Value, namely, 18.7 volume per cent.

VIII. UTILITY From the foregoing description, it will be apparent that the invention has considerable application in the chemical and related arts. For example, terminally sulfonated parains may be separated from the nonterminally substituted compounds in the manufacture of detergents and wetting agents by the sulfochlorination of parains. This makes possible purer and more ehicient detergents and wetting agents. Similarly, l-chloro straight chain parans may be separated from the corresponding non-terrninally substituted chloro compounds, which are formed in the chlorination of straight chain paraffitlins. Also, in the high temperature, vaporphase chlorination of olefins, two principal products are The addition of a mercaptan or hydrogen bromide to a l-oletin in the presence of air, oxygen or peroxides takes place with the addition of the mercapto radical, -SR, or bromo radical, -Br, to the terminal carbon atom of the olefin. If an olefin mixture containing a straight chain l-oleiin is so treated, the derivatives obtained from the straight chain l-olefn can be selectively separated by4 urea plexation. The l-olen derivatives obtained in this manner may be used for various purposes, or can be converted by known reactions to other useful products. For example, the bromide may be pyrolyzed to regenerate the pure 1olefin.

Not only are the separation procedures contemplated herein useful for removing substantial amounts of a contaminating constituent, as an isomer or isomers, from a related compound, but they are of value when small or trace amounts of such an undesirable constituent are present.

In addition, the new plexads made available herein constitute desirable sources of urea and `of the various plexands associated therewith. For example, the desired compounds can be kept in storage or shipped until just prior to use, when they are separated by reversion of the plexads.

Halogen compounds can be plexated from mixtures containing the same and form urea plexads, as described above and as described and claimed in application Serial No. 115,511, now abandoned. Sulfur-containing compounds are also plexated from their mixtures, and form plexads with urea, as described above and as described and claimed in application Serial No. 255,943, filed November 13, 1951, now Patent No. 2,681,336, as a continuation of application Serial No. 115,516 which has been abandoned. Plexation of compounds containing cyclic substituents, and urea plexads thereof, are described and are claimed in application Serial No. 116,593, now Patent No. 2,681,334; Plexation with urea of various terminally substituted compounds from mixtures containing the same and non-terminally substituted compounds, described above, is also described and is claimed in application Serial No. 115,517, now Patent No. 2,681,333.

Urea plexation of a non-terminally mono-substituted compound from mixtures containing the same and a non-terminally poly-substituted compound. is described and is claimed in application Serial No. 115,513, now Patent No. 2,642,422. Urea plexation of mixtures containing aliphatic compounds of different degrees of saturation is described and is claimed in application Serial No. 115,514, now abandoned; similarly, plexation of mixtures containing aliphatic hydrocarbons of different degrees of unsaturation and urea plexads of such hydrocarbons, are described and are claimed in application Serial No.115,518, now Patent No. 2,642,423 and in divisional application thereof Serial No. 266,547, tiled January 15, 1952.

Said applications Serial Nos. 115,511; 115,513; 115,514; 115,516 through 115,518 and 116,593 were filed concurrently on September 13, 1949 with application Serial No. 115,515, of which application this application is a continuation-impart.

I claim:

1. Crystalline complex of urea and a saturated straight chain mononitrile, in which the nitrile group is attached to a terminal carbon atom of the chain, in which the chain contains at least five carbon atoms, and which consists Aof the elements carbon, hydrogen and nitrogen.

2. Crystalline complex of urea and lauryl cyanide.

3. Crystalline complex of urea and a saturated straight chain mononitrile, in which the nitrile group is attached to other than a terminal carbon atom of the chain and in which the chain contains at least twenty-four carbon atoms, and which consists of carbon, hydrogen and nitrogen.

4. The method for selectively separating a saturated straight chain aliphatic mononitrile in which the nitrile 15 l@ group is attached to other than a terminal carbon atom References Cited in the file of this patent of the chain, in which the chain contains at least twenty- UNITED STATES PATENTS four carbon atoms, and which consists of the elements carbon, hydrogen and nitrogen, from a mixture contain- 2596344 Newey et al May 131 1952 ing the same and a compound incapable of forming a 5 OTHER REFERENCES complex with urea which comprises: contacting Said Die Harnstoi: Addition der aliphatischen Verbindunmixture with urea under conditions appropriate for the formation of a crystalline complex of urea and said mononitrile, whereby said complex is formed; and separating said complex from the resulting reaction mixture. 10

gen: Annalen der Chemie 565, part 3, pages 204-240 (1949), W. Schenk, Ir. 

1. CRYSTALLINE COMPLEX OF UREA AND A SATURATED STRAIGHT CHAIN MONONITRILE, IN WHICH THE NITRILE GROUP IS ATTACHED TO A TERMINAL CARBON ATOM OF THE CHAIN, IN WHICH THE CHAIN CONTAINS AT LEAST FIVE CARBON ATOMS, AND WHICH CONSISTS OF THE ELEMENTS CARBON, HYDROGEN AND NITROGEN.
 3. CRYSTALLINE COMPLEX OF UREA AND A SATURATED STRAIGHT CHAIN MONONITRILE, IN WHICH THE NITRILE GROUP IS ATTACHED TO OTHER THAN A TERMINAL CARBON ATOM OF THE CHAIN AND IN WHICH THE CHAIN CONTAINS AT LEAST TWENTY-FOUR CARBON ATOMS, AND WHICH CONSISTS OF CARBON, HYDROGEN AND NITROGEN. 